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Hades. Artwork of the hypothetical planet Hades, which is alleged to lie beyond the edge of the known solar system. Here it is comprised mainly of swirling gas, & is seen from a moon of rock & ice. Hades was first predicted by the German Theodor Grigull in 1902 to explain perturbations in the orbits of known planets. He based his work on the paths of comets whose orbits passed beyond the orbit of Neptune. In 1921 he suggested that Hades was about 14.5 times the mass of Earth and orbited every 310-330 years at a distance that was fifty times greater from the Sun than Earth. Extensive searches have failed to find such a planet, and it is unlikely to exist.
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